1. Field of the Invention
The present invention relates to an integrated communication system of voice and data, and in particular to an integrated communication system of voice and data which connects an Ethernet LAN to an external communication network.
Communication arts for a voice signal which is an analog signal and for data which is a digital signal have been developed individually. In the mean time, the voice signal has been able to be processed as voice data by converting the analog signal into the digital signal. Accordingly, in view of the advantages, a communication system which can process both signals in an integrated unit has been required.
2. Description of the Related Art
In a conventional office, as shown in FIG. 22, voice communication has been realized between a telephone terminal equipments TE and PBX (Private Branch exchange machine).
Data communication such as a mail or the like in the office has been realized by a LAN system of a client-server type in which a personal computer (PC) 2, a server 5, and a router 6 are mutually connected through an Ethernet LAN.
Outside the office, a voice signal is transferred from the PBX to a narrow band switching network (NBW NW) 10 through a pair of telephone stations circuits 9.
Also outside the office, the data communication has been realized by leading in a leased line network (LL NW) or a frame relay network (FR NW) 12 connected to other offices or internet network 14 into the office through the server 5 or the router 6. It is to be noted that the leased line network or the frame relay network 12 can be substituted by a narrow band switching network in case that data communication quantity outside the office is very little.
As a result, a personal computer and a telephone for voice communication to be connected to the LAN are required on a desk in the office, thereby narrowing an effective space on the desk. Also, a number of lines creep over the floor in the office. Although having been made smaller in size, the PBX accommodating several tens or hundreds of telephones is still large in size so that the office floor space for the PBX has to be wide.
Moreover, a lead-in wire from the outside of the office requires several pair wires or coaxial wires for the data communication in addition to voice pair wires.
Also, there has been increasing a case where a large quantity of data is taken in from a personal computer through internet WWW (World Wide Web) or the like. Therefore, the band of a communication circuit (line) which has been used for the conventional data communication will be narrowed, resulting in a long data communication time.
It is accordingly necessary to set up a new high-speed leased line after the abandonment of the conventional line and the peripheral system thereof so that the lead-in cost is increased burdening final users.
As a means for solving these problems, a skilled person in the art can conceive a method for making the whole including the office in the form of a wide band, as shown FIG. 23.
For example, in the office, an ATM switchboard (ATM-SW) 50 is provided having a function of LANE (LAN Emulation) such as LECS (LAN Emulation Configuration Server) 51, LES (LAN Emulation Server ) 52, BUS (Broadcast & Unknown Server) 53 and a function of MPOA such as an MPOA (Multi-Protocol Over ATM) servers 54, and leads in a personal computer PC using DS1 or ATM-25 interface (IF).
Circuits outside the office are led in a wide band public network (WB PUBLIC NW) 55 with an optical link through an ATM interface such as STS-1, DS3, or DS1, which forms a concept of B (broad band)-ISDN.
Also, as shown in FIG. 24, a skilled person in the art can conceive a method by which the data communication is carried out by using a high-speed LAN 60 in the office and by connecting the office to a wide band public network 55 outside the office with an optical link through a high-speed router 61 in the same as FIG. 23.
With regard to voice in these wide band systems, there is an idea achieved by VTOA (Voice Tele phony Over ATM) or the like.
However, in order to operate these systems, there costs a great deal of expense and remain technologically unsettled problems.
Furthermore, the public network also has a considerable difficulty in respect of technology and cost to contain the corresponding system, requiring a long term for the achievement.
Furthermore, it is necessary to abandon an existing system (such as a LAN system, a PBX, lead-in circuits, and a voice switchboard as well as the communication network on the public network side) or to invalidate the utilization for the system change.
Therefore, at the moment, those systems are impractical for a number of offices except big enterprises having a huge capital.
On the other hand, an internet telephone has been recently paid to attention as an art which transfers voice by incorporating a telephone in a personal computer to use an existing data communications system. As shown in FIG. 25, this art is to transfer voice data by using the protocol of TCP/IP for the internet where a connectionless UDP is actually used so that adverse effects on the existing system are little.
However, it is also necessary to set up a LAN system connected to the internet network 14 through an IP router 62 or the like to support the protocol of TCP/IP. In addition, the relay/DSP conversion process in a voice codec (CODEC) is mostly carried out by a processor (.mu. P), and therefore the personal computer is required to have a high-speed processor.
Moreover, the call quality depends on the status of data traffic in the internet network, and is not necessarily good as the evaluation is various. Because of the jammed condition caused, a condition may occur where the call is difficult to be made.
In any case, the internet telephone is poor concerning traffic managements in comparison with the conventional public telephone network while it is effective for a simple voice communication system. It is expected that a long term is required for the improvement including the solution of a basic problem.